Exam 20: Electric Fields and Forces

The three point charges +4.0 μC, -5.0 μC, and -9.0 μC are placed on the x-axis at the points x = 0 cm, x = 40 cm, and x = 120 cm, respectively. What is the x component of the electrostatic force on the -9.0 μC charge due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the center of the square?

Suppose you wanted to hold up an electron against the force of gravity by the attraction of a fixed proton some distance above it. How far above the electron would the proton have to be? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C², e = 1.6 × 10^-19 C, m_proton = 1.67 × 10^-27 kg, m_electron = 9.11 × 10^-31 kg)

What is the magnitude of a the vertical electric field that will balance the weight of a plastic sphere of mass $2.1 \mathrm {~g}$ that has been charged to -3.0 nC? (k = 1/4??₀ = 9.0 × 10⁹ N ? m²/C²)

Two point charges q = -8.50 µC are fixed 10.0 cm apart along a horizontal bar, as shown in the figure. Their electrical forces will be used to balance the weight of a very small sphere carrying a charge $Q = + 15.0 \mu \mathrm { C }$ 10.0 cm from each of them in a place where g = 9.80 m/s2. What is the greatest mass M this sphere can have without falling? (k = 1/4??₀ = 8.99 × 10⁹ N ? m²/C²)

Two equally charged tiny spheres of mass 1.0 g are placed 2.0 cm apart. When released, they begin to accelerate away from each other at $414 \mathrm {~m} / \mathrm { s } ^ { 2 }$ What is the magnitude of the charge on each sphere, assuming only that the electric force is present? (k = 1/4??₀ = 9.0 × 10⁹ N ? m²/C²)

An electric dipole consists of charges of ±6.00 µC that are 10.0 cm apart, as shown in the figure. Find the magnitude and direction of the electric field this dipole produces at point P, which is 7.00 cm from each charge. (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

Four point charges of equal magnitudes but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the center charge?

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z, or W)will the electron follow in the field?

Four point charges of equal magnitude but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the center charge?

Three equal-magnitude point charges of varying signs are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?

An asteroid of mass 58,000 kg carrying a negative charge of $15 \mu \mathrm { C }$ is $180 \mathrm {~m}$ from a second asteroid of mass $52,000 \mathrm {~kg}$ carrying a negative charge of $11 \mu \mathrm { C } .$ What is the magnitude of the net force the asteroids exert upon each other, assuming we can treat them as point particles? (G = 6.67 × 10^-11 N ? m²/kg², k = 1/4 ??₀ = 8.99 × 10⁹ N ? m²/C²)

Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the point charge with a charge +Q?

The figure shows two unequal charges, +q and -Q. Charge -Q has greater magnitude than charge +q. Point X is midway between the charges. In what section of the line will there be a point where the resultant electric field is zero?

Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?

Two large closely-spaced parallel metal plates are uniformly and oppositely charged and the electric field between them is 7.6 × 10⁶ N/C. (a)What is the charge per unit area on each plate? (b)If the plates are now moved two times farther apart, what is the electric field between the plates?

A conductor is placed in a steady external electric field. Which of the following statements are correct for this situation? (There could be more than one correct choice.)

Two uncharged metal spheres, #1 and #2, are mounted on insulating support rods. A third metal sphere, carrying a positive charge, is then placed near #2. Now a copper wire is momentarily connected between #1 and #2 and then removed. Finally, sphere #3 is removed. In this final state

Two tiny particles carrying like charges of the same magnitude are $1.0 \mathrm {~mm}$ apart. If the electric force on one of them is $5.0 \mathrm {~N}$ what is the magnitude of the charge on each of these particles?(k = 1/4??₀ = 9.0 × 10⁹ N ? m²/C²)

If a point charge of -30 µC experiences an electrostatic upward force of 27 mN at a certain location in the laboratory, what are the magnitude and direction of the electric field at that location?